This invention relates to low-loss non-imaging optical concentrators and more particularly to an infrared (xe2x80x9cIRxe2x80x9d) receiver optical system employed in remote control systems of multimedia projectors.
Projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. In the recent past, slide and overhead transparency projectors were commonly used for conducting sales demonstrations, business meetings, and classroom instruction. Slide projectors were commonly controlled by a remote control unit that was electrically connected to the slide projector by a cable that allowed a presenter, such as a salesperson, instructor, or project manager, to stand next to the projector or the projection screen while conducting the slide presentation. However, the cable limited the presenter""s mobility and presented a tripping hazard, especially in darkened rooms.
More recently, slide and overhead presentations have been largely replaced by presentations employing multimedia projection systems. In a typical operating mode, multimedia projection systems receive video signals from a personal computer (xe2x80x9cPCxe2x80x9d), a tape drive, a disk drive, or some other form of image generating or storing device. The video signals may represent still, partial-, or full-motion display images of a type typically rendered by PCs. The video signals are converted in the multimedia projection system into signals that control a digitally driven imaging device that forms the image to be projected.
The presenter typically controls the multimedia projection system with a wireless IR remote control device similar to ones employed to control home television receivers. This has greatly increased the mobility of the presenter and eliminated the tripping hazard. In fact, multimedia projectors have grown in popularity to the point where they are available in diverse models suited for, among others, portable, tabletop, ceiling-hung, and rear-projected applications.
Because battery powered IR remote control devices are typically quite directional, the wide variety of possible projector placements and various possible presenter positions causes a dilemma. The presenter can usually point the IR remote control transmitter toward the multimedia projector, but proper placement of the IR receiver on the multimedia projector is indeterminate. Suitable IR receiver mounting positions may include top mounting when the presenter is standing close to the multimedia projector, front mounting when the presenter is standing near the projection screen, and rear mounting when the presenter is behind the multimedia projector. Top mounting may also be suitable in ceiling-hung applications in which the multimedia projector is hung upside down. Clearly no single IR receiver position was suitable for all applications, so prior workers placed multiple IR receivers on the major surfaces of the multimedia projectors, an unduly complex and costly solution.
Prior IR receivers are directional primarily because the optical components coupling IR energy to an IR sensor have a limited range of angular coverage. Indeed, the most common optical component is merely an optical window having a spectral filtering property that improves the signal-to-noise ratio of the sensed IR energy. Attempts to compensate for the directionality of prior IR receivers included increasing IR transmitter power and/or IR receiver sensitivity. Unfortunately, the former solution unacceptably increased battery consumption and the latter solution was marginal because receiver sensitivity was already typically maximized. In response to this need, prior workers developed an IR receiver employing an omnidirectional optical concentrator coupled to a single IR sensor having usable sensitivity to received IR energy over a wide range of azimuthal and elevation angles. This system is described in U.S. Pat. No. 6,201,246 for NON-IMAGING OPTICAL CONCENTRATOR FOR USE IN INFRARED REMOTE CONTROL SYSTEMS, which is assigned to the assignee of this application.
A problem with the above-described system is that the omnidirectional optical concentrator is mounted on the projector case and the IR sensor is mounted on a circuit board inside the projector. Manufacturing tolerances require a gap between the concentrator and the sensor, which gap creates multiple reflections of the IR signal that increases transmission loss in the system, thereby reducing the effective range of the IR remote control.
What is still needed, therefore is an IR receiver having increased sensitivity to received IR energy over a wide range of azimuthal and elevation angles.
An object of this invention is, therefore, to provide an apparatus and a method for efficiently receiving light rays propagating from multiple angles and directing them toward a light sensor.
Another object of this invention is to provide a low-loss non-imaging optical concentrator apparatus.
A further object of this invention is to provide an omnidirectional IR receiver usable with a remote controller in a multimedia projection application.
A non-imaging optical concentrator receives light rays propagating from a wide range of elevational and azimuthal angles relative to an optical axis and directs them through a low-loss medium toward a light sensor. A first embodiment of the optical concentrator includes an optically transparent body including a substantially dome-shaped convex surface of revolution formed about the optical axis and a conical concave surface of revolution formed about the optical axis and protruding into the convex surface in a direction along the optical axis in a direction toward the light sensor. The convex surface receives light rays propagating from low elevational angles and causes them to propagate through the optically transparent body, reflect off the concave surface, and propagate generally along the optical axis toward the light sensor. The concave surface further receives light rays propagating from high elevational angles and refracts them through the optically transparent body toward the light sensor. In this embodiment, the non-imaging optical concentrator is mounted to a multimedia projector housing, and the light sensor is mounted on a circuit board within the projector housing. The concentrator and housing are separated by about a 1 millimeter gap.
A second embodiment of the optically transparent body further includes a second conical concave surface of revolution formed about the optical axis and protruding from near the apex of the first conical concave surface deeper into the optically transparent body in a direction along the optical axis. The convex surface further receives light rays propagating from medium elevational angles and causes them to propagate through the optically transparent body and reflect at relatively low angles off the first and second concave surfaces in a direction generally along the optical axis toward the light sensor. In a manner similar to the first concave surface, the second concave surface further receives light rays propagating from high elevational angles and refracts them through the optically transparent body toward the light sensor. In this embodiment, the non-imaging optical concentrator is mounted to the circuit board within the projector housing and protrudes through a hole in the housing. The light sensor is also mounted to the circuit board, but because of alignment and manufacturing tolerances, is still separated from the concentrator by the gap.
This invention increases light transmission between the concentrator and the light sensor inserting a soft, pliable, optically clear light transmission medium in the air gap. The light transmission medium reduces IR transmission losses by eliminating the multiple reflections caused by material-to-air interfaces. The light transmission medium is preferably a soft material, such as silicon gel or silicon glue, that is constrained by an annular ring of rigid material to hold the light transmission medium in place during the manufacture and useful lifetime of the projector.
In an alternative embodiment of this invention, the optical concentrators include a recess in the surface facing the gap. The soft, pliable light transmission medium is inserted into the recess and allowed to protrude by an amount that gently compresses it against the light sensor.
The low-loss non-imaging optical concentrators of this invention is advantageous because only one light sensor is required to receive IR controller data propagating from a wide range of distances, elevational angles, and azimuthal angles. They are, therefore, particularly useful for use in multimedia projector applications.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof that proceeds with reference to the accompanying drawings.